Basic Idea:
I want to encourage my users to post more comments, but the problem is that many users don't want to register to my blog for different reasons. On the other hand I want to be able to ban users once they start to spam or misbehave otherwise, but approving each and every comment takes a lot of time. This is also bad for discussing a post within the comments.

Solution:
This problem would be (mostly) solved, if I need to approve an registered user only once, _but!_ still have approve every comment from a not-registered user.

At the moment it is impossible to distinguish between this two groups in comment-moderation.

There is a hack around that enables me to auto-approve every comment for a certain role, including the first one. The "Role approved comment" doesn't seem to work properly atm, and has the same problem as the hack.